This invention has to do primarily but not exclusively with drive trains for tracked vehicles, and has particular application to vehicles such as the ones shown and described in U.S. Pat. No. 4,795,222.
The conventional drive train of such tracked vehicles is illustrated in FIG. 1. As shown there, a drive train 1 includes a differential 2 from which a spline shaft 16 extends through a hollow spindle 3 that is fixed against rotation. The spindle 3 has a spindle flange 4 on it, to which a housing carrier 5 is bolted. A housing 6 is rotatably journaled on the housing carrier 5. A flange 7 projects radially outwardly from the housing, and has studs extending axially from it to which a sprocket mount 8 is attached by nuts 10, This is also shown in FIG. 3. The sprocket mount 8 includes a sprocket flange 9 through which the bolts extend, an annular base 11 secured to the flange 9, and spaced annular walls 12, between which cross bars 13 extend for reinforcement. The walls 12 are undular, as shown in FIG. 3. Urethane sprockets 14, which in the conventional drive are uninterrupted, are bolted to the two outwardly facing sides of the walls 12, as shown in FIG. 1, by means of bolts 15.
It can be seen by comparing FIG. 1 of the present application with FIG. 1 of Pat. No. 4,795,222, that the track extends in both directions transversely of the sprockets, and that the sprocket engages grouser bars of the track. In the conventional construction described, this permits rocks and earth to accumulate between the track and the housing, which projects a substantial distance beyond the outboard side of the sprocket. The construction of the sprocket itself, with two spaced sections and a substantial gap between them, makes for rapid wear, which permits the steel walls 12 to engage the grouser bars, thus causing the grouser bars to fail. Rocks and debris get between the gear shaped metal surfaces and the track, sometimes causing bending and failure of the metal drive sprocket. The internal dimensions of the housing severely limit the amount of reduction that can be obtained in the outboard planetaries, and also limits the strength of the various gears. When the amount of reduction of the planetaries is low, more reduction is required in the differential, which makes braking and steering more difficult and increases the strain, hence the wear and tear, on the components of the drive system. The sun gear is conventionally splined or keyed to the end of the spline shaft. Also, conventionally, a threaded plug is provided in the cover of the housing, which has to be removed, and a dip stick or one's finger inserted, to determine the oil level in the housing. This discourages frequent checking, and leads to the provision of an inadequate amount of oil, and consequent damage to the gears.